Highway snow and ice control typically is carried out by governmental authorities with the use of dump trucks which are seasonally modified by the addition of snow-ice treatment components. These components will include the forwardly-mounted plows and rearwardly-mounted mechanisms for broadcasting materials such as salt or salt-aggregate mixtures. The classic configuration for the latter broadcasting mechanisms included a feed auger extending along the back edge of the dump bed of the truck. This hydraulically driven auger effects a metered movement of material from the bed of the truck onto a rotating spreader disk or "spinner" which functions to broadcast the salt across the pavement being treated. To maneuver the salt-based material into the auger, the dump bed of the truck is progressively elevated as the truck moves along the highway to be treated. Thus, when into a given run, the dump bed will be elevated, dangerously raising the center of gravity of the truck under inclement driving conditions.
An initial improvement in the controlled deposition of salt materials and the like has been achieved through the utilization of microprocessor driven controls over the hydraulics employed with the seasonally modified dump trucks. See Kime, et al. in U.S. Pat. No. Re33,835, entitled "Hydraulic System for Use with Snow-Ice Removal Vehicles", reissued Mar. 3, 1992. This Kime, et al. patent describes a microprocessor-driven hydraulic system for such trucks with a provision for digital hydraulic valving control which is responsive to the instantaneous speed of the truck. With the hydraulic system, improved controls over the extent of deposition of snow-ice materials is achieved. This patent is expressly incorporated herein by reference.
Investigations into techniques for controlling snow-ice pavement envelopment have recognized the importance of salt in breaking the bond between ice and the underlying pavement. Without a disruption of that bond, little improvement to highway traction will be achieved. For example, the plow merely will scrape off the snow and ice to the extent possible, only to leave a slippery coating which may be more dangerous to the motorist than the pre-plowed road condition.
When salt has been simply broadcast over the pavement from a typical spinner, it will have failed to melt sufficient ice to break the ice-road bond. The result usually is an ice coated pavement, in turn, coated with a highly dilute brine solution developed by too little salt, which will have melted an insufficient amount of ice for traction purposes. This condition is encountered often where granular salt material contains a substantial amount of "fines". Fines are very small salt particles typically generated in the course of transporting, stacking, and storing road maintenance salt in dome-shaped warehouses and the like.
Road snow-ice control studies have revealed that the activity of ice melting serving to break the noted ice-pavement bond is one of creating a saltwater brine of adequate concentration. In general, an adequate salt concentration using conventional dispersion methods requires the distribution of unacceptable quantities of salt on the pavement. Some investigators have employed a saturated brine as the normal treatment modality by simply pouring it on the highway surface from a lateral nozzle-containing spray bar mounted behind a truck. A result has been that the thus-deposited brine concentration essentially immediately dilutes to ineffectiveness at the ice surface, with a resultant dangerous liquid-coated ice highway condition.
Attempting to remove ice from pavement by dissolving the entire amount present over the entire expanse of pavement to be treated is considered not to be acceptable from an economical standpoint. For example, a one mile, 12 foot wide highway lane with a 1/4 inch thickness of ice over it should require approximately four tons of salt material to make a 10% brine solution and create bare pavement at 20.degree. F. Technical considerations for developing a salt brine effective to achieve adequate ice control are described, for example, by D. W. Kaufman in "Sodium Chloride: The Production and Properties of Salt and Brine", Monograph Series 145 (Amer. Chem. Soc. 1960).
The spreading of a combination of liquid salt brine and granular salt has been considered advantageous. In this regard, the granular salt may function to maintain a desired concentration of brine for attacking the ice-pavement bond and salt fines are more controlled by dissolution in the mix. The problem of excessive salt requirements remains, however, as well as difficulties in mixing a highly corrosive brine with particulate salt. Typically, nozzle injection of the brine is the procedure employed. However, attempts have been made to achieve the mix by resorting to the simple expedient of adding concentrated brine over the salt load in a dump bed. This approach is effective to an extent. However, as the brine passes through the granular salt material, it dissolves the granular salt such that the salt will not remain in solution and will recrystallize, causing bridging phenomena and the like inhibiting its movement into a distribution auger. Of course, the corrosive effect of the liquid brine upon the relatively mild steel forming the truck dump bed is not appreciated by truck operators.
The problem of the technique of deposition of salt in a properly distributed manner upon the highway surface also has been the subject of investigation. Particularly where bare pavement initially is encountered, snow/ice materials utilized in conventional equipment will remain on the highway surface at the time of deposition only where the depositing vehicles are traveling at dangerously slow speeds, for example about 15 mph. Above those slow speeds, the material essentially is lost to the roadside. Observation of materials attempted to be deposited at higher speeds shows the granular material bouncing forwardly, upwardly, and being broadcast over the pavement sides such that deposition at higher speeds is ineffective as well as dangerous and potentially damaging to approaching vehicles. That latter damage sometimes is referred to as "collateral damage". However, the broadcasting trucks themselves constitute a serious hazard when traveling, for example at 15 mph, particularly on dry pavement, which simultaneously is accommodating vehicles traveling, for example at 65 mph. The danger so posed has been considered to preclude the highly desirable procedure of depositing the salt material on dry pavement just before the onslaught of snow/ice conditions. Of course, operating at such higher speeds with elevated dump truck beds also poses a hazardous situation.
Kime, et al., in U.S. Pat. No. 5,318,226 entitled "Deposition of Snow-Ice Treatment Material from a Vehicle with Controlled Scatter", issued Jun. 7, 1994, (incorporated herein by reference) describes an effective technique and mechanism for controlling the scatter of the so-called granules at higher speeds. With the method, the salt materials are propelled from the treatment vehicle at a velocity commensurate with that of the vehicle itself and in a direction opposite that of the vehicle. The result is an effective suspension of the projected materials over the surface under a condition of substantially zero velocity with respect to or relative to the surface of deposition. Depending upon vehicle speeds desired, material deposition may be provided in controlled widths ranging from narrow to wider bands to achieve a control over material placement. Another "zero-velocity" method for salt distribution employing a different apparatus approach has been introduced by Tyler Industries, Inc. of Benson, Minn. See "Roads & Bridges", December 1995, Scranton Gillette Communications, Inc., Des Plaines, Ill.
Thus, while the difficulties attendant with broadcasting granular salt at more acceptable highway speeds have been addressed with some success, the technical challenge of breaking the ice-pavement bond with a practical quantity of salt such that motor vehicles may achieve adequate traction has remained an elusive goal.